Endometrial ablation is a common surgical procedure that is used to treat menorrhagia in women, which is typically accomplished through the application of either sufficiently hot or sufficiently cold temperatures to destroy the lining of the uterus. One type of procedure used for endometrial ablation involves the use of a device that rolls over the surface of the uterine wall while applying enough heat to destroy the endometrial tissue. While this type of procedure can be effective, it requires a significant amount of time and skill in anipulating the rolling device to ensure that the entire endometrium is destroyed.
Another type of procedure used for endometrial ablation also uses heat, but instead involves balloons or similar distensible bladders. These balloons are inserted into the uterus and inflated with a fluid until the balloon contacts the affected surfaces of the uterus. Fluid is then heated to an appropriate temperature to ablate or destroy the endometrium. Good surface contact is important to get complete coverage of the uterine lining. However, such coverage can be difficult due to temperature fluctuations and gradients along the surface of the balloon that can be caused by any factors, such as convective currents of the fluid within the balloon. To improve control of the fluid temperature within the balloon, various mechanical devices and systems have been used for circulating or agitating the heated fluid, such as through multiple fluid passageways, propellers within a lumen contained within the balloon, vibrating members, and electrical impulses. These mechanical devices or systems provide varying degrees of effectiveness, depending on the administrator of the procedure and the device itself. In addition, the movement of hot fluid into the balloon can sometimes cause discomfort or possible tissue damage to the vagina and opening of the cervix as heat is conducted through the walls of the catheter to which the balloon is attached.
Another group of procedures used for endometrial ablation involves the application of extremely low temperatures and is commonly referred to as cryosurgery. In the performance of cryosurgery, it is typical to use a cryosurgical application system designed to suitably freeze the target tissue. The abnormal or target cells to be destroyed are often surrounded by healthy tissue that should be left uninjured. Many of these systems use a probe with a particular shape and size that is therefore designed to contact a selected portion of the tissue that is to be treated without undesirably affecting any adjacent tissue or organs. In one particular application used to treat conditions of abnormal uterine bleeding, cryoablation instruments and techniques are used to freeze endometrial tissue, thereby destroying at least a portion of the endometrium or lining of the uterus, while leaving the remainder of the uterus undamaged. An example of a device that can be used for this type of cryoablation is the Her Option Cryoablation System, commercially available from American Medical Systems of Minnetonka, Minn. In this type of system, a rigid probe is provided with a very cold tip that freezes the endometrial tissue with which it comes in contact. Where such a probe is used, the remainder of the refrigeration system must be designed to provide adequate cooling, which involves lowering the operative portion of the probe to a desired temperature and having sufficient power or capacity to maintain the desired temperature for a given heat load. The entire system must be designed so that the operative portion of the probe can be placed at the location of the tissue to be frozen without having any undesirable effect on other organs or systems. For this reason, probes in these types of systems are often in the shape of an elongated tube with a rounded tip area at one end that can be positioned within the uterus for the cryoablation procedures. Other cryocooling surgical devices, components thereof, and surgical methods are disclosed in U.S. Pat. Nos. 5,275,595; 5,758,505; 5,787,715; 5,901,783; 5,910,104; 5,956,958; 6,035,657; 6,074,572; 6,151,901; 6,182,666; 6,237,355; 6,241,722; 6,270,494; 6,451,012; 6,471,217; 6,471,694; 6,475,212; 6,530,234; and 6,537,271, each of which is incorporated by reference in its entirety.
In many cases, the cold portion of an instrument or device is provided through the use of a Joule-Thompson refrigeration system. These refrigeration systems generally operate through the expansion of a high-pressure gas through an expansion element that includes some sort of a flow restrictor. The restriction of flow ay be accomplished through the use of a small orifice, a narrow capillary tube, or some other sort of passage that is smaller than the supply source through which the high-pressure gas must move. Typically, the refrigeration system includes a source of high-pressure gas, a heat exchanger, an expansion element, a heat transfer element, and various tubes or conduits that allow movement of the gas from one component to another. The high-pressure gas passes through the heat exchanger to lower the gas temperature at least slightly, then the gas temperature is further lowered through the isenthalpic expansion of the gas as it passes through the expansion element. This expanded and cooled gas is exposed to the heat transfer element, where the gas can then absorb the heat that has been transferred from the environment.
In most systems, the cooling tip is designed or chosen to be small enough to easily be accurately positioned at the treatment area, which generally limits the technique to applying the cooling to a relatively small area with each placement of the probe. The entire process thus typically requires that the probe be positioned at least two or three times to ablate the entire target area, such as an entire uterine cavity. Each relocation of the probe requires repetition of the same cooling steps, which can be time consuming and requires multiple precise placements of the probe to guarantee that the entire area is adequately ablated.
With these cryosurgical techniques, it is typically desirable to insulate the shaft of a cryosurgical probe to prevent the unintentional freezing of tissue at locations along the length of the probe that may inadvertently or unavoidably come in contact with the probe shaft. One way these shafts are often insulated is to provide a vacuum space along the probe shaft. This method is sometimes ineffective because the level of the vacuum maintained in such a space can degrade over time due to the outgassing of etals, plastics, and braze joints. This outgassing can increase during sterilization procedures in which heat is applied to the probe. Thus, it is known to incorporate the insulation into a disposable sheath that can be disposed over a probe, as is described in U.S. Pat. No. 6,182,666 (Dobak III), for example, so that the disposable element is not subjected to repeated sterilization, but instead can be discarded without significant degradation of the insulation. This disposable sheath can be constructed of a thermally resistive material, such as a plastic, to inhibit heat transfer between the surrounding tissues and the probe that it covers.
There is, however, a need to provide a system and device for endometrial ablation using cryosurgical methods that improve the overall coverage of the endometrial surface for a range of uterine sizes and shapes while maintaining an appropriate depth of ablation. There is further a need for these systems and devices to be easily manipulated to the affected areas, while having the ability to quickly generate an appropriately sized cold area or ice ball within the uterus for ablation. In addition, these systems will desirably include an efficient heat exchanger that provides improved cooling power with a given amount of input energy.